Object acquisition is carried out via an extendable
probe carrying a mirror feeding a Westinghouse ISEC TV camera.
When used direct ( not the usual mode of acquisition when ISIS is in
use),
this provides a 1.5 arcmin field at the telescope scale of 4.51
arcsec/mm. It is possible to insert a focal reducing system,
which provides a larger field of 4 arcmin at a scale of
12 arcsec/mm. The TV camera is provided
with a filter wheel with six filter positions.
The available filters are CLEAR (UBK7), B (BG 28), V (BG 38), R (RG 630)
and EMPTY (no filter). Note that the empty position will give a different
focus position for the TV. These filters do not give a standard
photometric system and the Johnson letters are given for guidance only.

The TV can be focussed independently to compensate for different filter
thicknesses.